In earlier studies, we have observed that allergen inflammation, induced either by allergen challenge or by natural exposure to aeroallergens during pollination seasons, enhances neutrophil influx to airway mucosal tissues following endotoxin challenge. We have also found that pre-challenge expression of CD14 on airway macrophages correlates strongly with neutrophil influx following endotoxin challenge and with baseline levels of eosinophils in the airway, and the treatment with inhaled corticosteroids decreases baseline eosinophil and macrophage CD14 expression and blunts response to endotoxin. We have also observed that repeated challenge with endotoxin induces tolerance to endotoxin, a phenomenon that, in animals, is reversed by GM-CSF, a product of TH2 inflammation. These findings support the hypothesis that allergic inflammation enhances response to endotoxin. Our proposal to continue these studies focuses on in vivo studies in human volunteers to examine the effect of allergen-induced inflammation on airway macrophage expression of molecules important in mediating endotoxin responsiveness and the effect of allergen challenge on bronchial response to inhaled endotoxin. We will also focus on development of tolerance to endotoxin in the bronchial airway, and assessment of CD14, TLR4, IL-1 receptor associated kinase, I?B and other mediators or modulators of endotoxin signal transduction in airway macrophages from persons undergoing a tolerance-inducing endotoxin challenge. We will also employ nasal challenge and in vitro studies of monocytic cells to examine the effect of GM-CSF and other candidate cytokines produced by IgE-mediated inflammation on in vivo and in vitro response to LPS